The odds are Probably... 1/64 - KQ Head 1/128 - KBD Head 1/256 - Big Shark 1/512 - Big swordfish/Big Bass 1/1024 - Abyssal Demon, Kurask, Cockatrice, Basilisk and Crawling hand. That's based on what people have been saying, and to me, those odds look correct. KQ Head, about the same rarity was Dragon Chain. KBD Head, About the same rarity as Med. Shark - Hard to catch anyway, so 1/256 is about right. 1/512 for Swordfish/Bass seems accurate. The slayer monsters are about 5-7x as rare as that monsters "rare" drop. (Whip, Mystic Top, Mystic boots, Mystic hat and uhh Nothing :P